This invention relates to optical dosimeters, which utilize the darkening induced in various glasses and other optical materials by ionizing and nuclear radiation to measure the radiation dose.
The darkening of optical materials upon exposure to ionizing and nuclear radiation is a well-known phenomenon. Glasses, in particular, have been successfully employed in block form as radiation dosimeters for high dose levels (Klaus Becker, Solid State Dosimetry, CRC Press, Cleveland, Ohio, 1973). These materials have usually contained additives such as silver or cobalt to sensitize, control and stabilize the coloration process. However, the poor optical quality and limited size of the glass block dosimeters have restricted the application of these devices.
The use of glass optical fibers as a solution to the problems encountered with bulk glass dosimeters is described in two papers from the Naval Research Laboratory; one on "Glass Fiber-Optic Dosimetry" by Bruce D. Evans on pages 88-93 of Vol. 77 (1976)--Fibers & Integrated Optics, by the Society of Photo-Optical Instrumentation Engineers, Box 1146, Palos Verdes Estates, Calif. 90274; and the other on "The Fiber Optic Dosimeter on the Navigational Technology Satellite" by B. D. Evans et al in IEEE Transactions on Nuclear Science, Vol. NS-25, No. 6, December 1978, pages 1619-1624. These two papers are incorporated by reference. A combination of low intrinsic optical loss and greatly increased optical path length with optical fibers permit enhanced radiation sensitivity of at least one hundred times greater than the conventional glass block dosimeters. In addition, because of the flexibility and small size of the fibers, the sensing element can be confined to a very small volume and is of negligible weight.
However, some crystalline radiation sensitive materials are not readily amenable to drawing into optical fibers.